The design and construction of communication vehicles for receiving and/or transmitting signals requires consideration of numerous parameters, many depending upon the particular application to which the vehicle is being put. For example, weight and balance, axle loading, generator enclosure area, roadability, safety and weather integrity must be carefully considered for each vehicle being designed and built.
One critical component of communication vehicle designs is the antenna. During operation, the height of the antenna relative to the earth must be sufficient to allow for suitable transmission and/or receipt of signals regardless of the location of the vehicle. Such heights often exceed 40 feet. As a result, it is desirable that the antenna be capable of being oriented from its operating or "up" position, to a retracted or "down" position affording reduced air resistance and reduced potential for damage from overhanging obstacles during movement of the vehicle from site to site. Indeed, overall height is restricted by the U.S. Department of Transportation to 13'6".
To that end, pneumatically operated systems conventionally have been employed. However, numerous problems with such devices have arisen. For example, a compressor is necessary to pressurize the entire mast assembly. Over time, leaks develop in the system, resulting in the slow lowering of the mast during operation. If the compressor is designed to switch on upon sensing such lowering, there may be a sudden spike in electrical power which could interfere with the signals being transmitted from or received in the vehicle. Since the mast is lowered by gravity, if the antenna is in the operating up position during an ice or snow storm, freezing of the retractable components can occur, making it impossible to retract the antenna and therefore to move the vehicle.
Other components of other vehicles, such as lighting towers, that are mounted on the vehicle and adapted to extend upwardly suffer from similar difficulties.
It is therefore an object of the present invention to provide a power mast that eliminates the foregoing drawbacks.
It is a further object of the present invention to provide a power mast that automatically elevates and retracts an antenna or other device quickly and easily without pressurizing the system.